Using the sun and wind is an ecologically safe method for producing power.

Long ago, people learned to use wind power.
Windmills which were widely used in the past convert the power of an air stream into the rotation of useful mechanisms. At the present time, the half-forgotten technology revives. In Holland, one can see numerous huge windmills beating the air with their carbon plastic wings on the seacoast. It is always windy near the sea but the wind speed is limited whereas a windmill requires a very strong wind.
Today, another natural resource – the sun – becomes increasingly important for producing electric power. Solar cells can convert light beams directly into electric power. Though solar power is free, solar cells themselves are expensive devices. Researchers work on reducing the solar cell cost. Using the sun and wind is an ecologically safe method for producing power.
How does wind arise? Certainly not because trees rock. The sun heats the earth non-uniformly. As a result, warm air from heated portions rises to be replaced with cold air.

This effect was used by Australian scientists. They developed a project of an ecologically safe power station where wind is produced by the sun action. The power station is a huge (20 000 acres) round field covered with a transparent film. There is a vertical 1 km tall chimney installed in the center of this gigantic green house. Turbines and generators are mounted at the chimney end.
The sun heats the air under the film. The air rises through the chimney. At the top of the chimney, the vertical air current reaches the force of a hurricane and rotates the turbines which produce electric power. In the estimation of specialists, such a power station can provide 800 000 houses with electric power.

Combining the alternative systems gave rise to an effective principle of electric power production.